STS-112's
primary payload is the S1 (S-One) Truss, which will be attached
to the International Space Station and outfitted during three
spacewalks. The S1 is 13.7 meters (45 feet) long and weighs about
13.6 metric tons (15 tons). It will be the third component of
the 11-piece Integrated Truss Structure delivered to the station
and will allow for the outward expansion of the station. The S1
will be attached to the S0 (S-Zero) Truss' starboard side.

The large
truss contains: a new external cooling system for the station
that is slated to be activated in 2003; a second S-Band communications
system to provide enhanced and extended voice and data capability;
a cart that will serve as a mobile work platform for future spacewalkers;
two new external television cameras; and the first Thermal Radiator
Rotary Joint, which will provide the mechanical and electrical
energy for rotating the station's heat-rejecting radiators based
on various system requirements.

The S1's
attachment to the station is slated to occur during Flight Day
4.

What
is a payload?

The
formal designation as a "payload" indicates that the experiment
will be accorded top priority in crew time and energies during the
entire flight, along with all other experiments carrying the same
"payload" designation.